1. Field of the Invention
The present invention relates to a varnishing installation having a varnish line with an inlet end, an outlet end and an auxiliary device.
2. Description of the Related Art
Before cleaning a varnish line, it is in many cases desirable to recuperate any varnish residues in the varnish line which have been left over from a previously carried out varnishing process. Used for this purpose is a so called scraper which is pushed through the varnish line against the direction of flow of the varnish during varnishing. The scraper rests against the inner side of the varnish line and at least substantially “scrapes” clean the inner wall of the line. Of course, in addition to the recuperation of varnish residues which remain after a varnishing process at the inner wall of the varnish line, the use of a scraper for precleaning the varnish line also has the advantage that during a subsequent rinsing process less rinsing agent will be needed and the rinsing agent is only contaminated to a small extent.
The use of a scraper is primarily advantageous if a frequent change of color is to be carried out during the varnishing of structural components. This situation occurs frequently in the automobile industry. In that case, the varnish line is arranged between a source which is frequently formed by a ring line arrangement in which several color lines are arranged in a ring shape, and wherein a specific varnish is circulated in each color line. These color lines supply a so called color changer from which the color varnish intended for the varnish application is supplied to the atomizer within the varnishing cabin. The outlet end of the varnish line between the color changer and the atomizer is then located in a varnishing cabin in which the actual varnish application takes place.
The use of a scraper and a scrapeable line is known.
However, an auxiliary device is necessary in many varnish lines. This auxiliary device may have various configurations. For example, the auxiliary device may be a pump which raises the pressure of the varnish between the inlet end and the outlet end in order to facilitate varnishing by means of a spray application at a higher pressure. In accordance with another embodiment, the auxiliary device may be a high-voltage arrangement which serves to raise the electrical potential of the varnish. These two embodiments are merely examples.
When such an auxiliary device is provided in the varnish line, the use of a scraper becomes more difficult. The auxiliary device usually has many difficult locations, i.e., corners and edges, so that the scraper would be damaged if it were moved through the auxiliary device. Also, in many cases the free cross-sectional area of the varnish line is reduced, for example, when the auxiliary device is a gear pump.
Therefore, depending on the arrangement of the auxiliary device, precleaning of the varnish line by means of a scraper must be terminated in front of or behind the auxiliary device. This means that an area remains between the auxiliary device and the inlet end in which the varnish cannot be removed. As an alternative, the application of the scraper is restarted in this area, or scrapers are used which are allowed to wear quickly.